Gas flow behavior modeling method, device, design method and system

Abstract

The invention discloses a gas flow behavior modeling method, device, design method and system. The modeling method comprises the following steps: acquiring partition information of a plurality of partitions in a vacuum system of a mass spectrometer; and respectively establishing a gas flow state model of each partition according to the partition information. And according to the partition information and the gas flow state model of each partition, an effective pumping speed model of each partition is established. And simultaneously establishing the effective pumping speed models of the partitions to obtain a gas flow behavior model in the mass spectrometer vacuum system. According to the modeling method, the airflow behavior of the pipeline of the vacuum system of the mass spectrometer can be accurately modeled.

Description

Technical Field

[0001] The present invention specifically relates to a method for modeling gas flow behavior in a mass spectrometer vacuum system, a method for designing a mass spectrometer vacuum system, a device for modeling gas flow behavior in a mass spectrometer vacuum system, a design system for a mass spectrometer vacuum system, and a mass spectrometer vacuum system. Background Art

[0002] Thermal ionization mass spectrometer (TIMS) is mainly composed of ion source, magnetic field mass analyzer, detector system, vacuum system, measurement and control and software system.

[0003] Among them, the vacuum system is the key part of the thermal ionization mass spectrometer. A high vacuum environment is the basis for the operation of the thermal ionization mass spectrometer. A good vacuum system can create a long mean free path and a chemically clean environment for ions, avoiding ion optical contamination and signal loss caused by collisions between charged ions and background gases and various lenses.

[0004] However, due to the complex gas flow in the vacuum system pipelines, current mass spectrometers are unable to accurately model and calculate the complex flow patterns of gas in the vacuum pipelines when designing the vacuum system. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a gas flow behavior modeling method, device, design method and system in view of the above-mentioned deficiencies in the prior art. The modeling method can accurately model the gas flow behavior of the pipeline of the vacuum system of the mass spectrometer.

[0006] According to an embodiment of the first aspect of the present invention, a method for modeling gas flow behavior in a vacuum system of a mass spectrometer is provided, wherein the vacuum system of the mass spectrometer has a plurality of partitions, and the plurality of partitions are sequentially connected, and the method comprises the following steps:

[0007] obtaining partition information of a plurality of partitions in a vacuum system of a mass spectrometer;

[0008] According to the partition information, a gas flow model of each partition is established respectively;

[0009] According to the partition information and the gas flow model of each partition, an effective pumping speed model of each partition is established respectively;

[0010] The effective pumping speed models of each partition are combined to obtain the gas flow behavior model in the mass spectrometer vacuum system.

[0011] Preferably, the partition information includes gas characteristic parameters, geometric parameters and pumping speed characteristic parameters;

[0012] The gas characteristic parameters include: gas viscosity η, gas density ρ, gas flow rate v, and gas pressure value p;

[0013] The geometric parameters include: the equivalent diameter d of the partitioned pipeline cross section;

[0014] The pumping speed characteristic parameters include: a pump inlet air pressure value, an air pressure value inside a partition, a volume flow value at the pump inlet, and a leakage rate within the partition.

[0015] Preferably, the step of establishing the gas flow model of each partition according to the partition information comprises:

[0016] Analyzing the airflow state in each partition according to the gas characteristic parameters and geometric parameters;

[0017] According to the airflow state in each partition, the gas flow model of each partition is established respectively.

[0018] Preferably, the step of establishing a gas flow model for each partition according to the gas flow state in each partition comprises:

[0019] Determine in turn whether the airflow state in each partition is the first flow state or the second flow state:

[0020] When the gas flow state in the partition is a first flow state, the gas flow state model adopts a Reynolds number expression, and the first flow state is a turbulent state;

[0021] When the gas flow state in the partition is the second flow state, the gas flow state model adopts the Knudsen number expression, and the second flow state is a viscous flow, a molecular flow or a transitional flow state.

[0022] Preferably, the Reynolds number expression is:

[0023]

[0024] Where Re is the Reynolds number; η is the gas viscosity; ρ is the gas density; v is the gas flow rate;

[0025] The Knudsen number expression is:

[0026]

[0027] Where Kn is the Knudsen number; v is the gas flow rate; η is the gas viscosity; p is the gas pressure value; d is the equivalent diameter of the partitioned pipe cross section.

[0028] Preferably, the effective pumping speed model includes:

[0029] Q=P·S eff ·F(Kn)

[0030] F(Kn)=1+α·Kn

[0031] S eff =S0·(1-β·f(Re))

[0032] Q=P·S0·(1-β·f(Re))·(1+α·Kn)

[0033] Where Q is the leakage rate in the partition; P is the pressure in the system; S eff is the effective pumping speed; F(Kn) is the correction term dependent on the Knudsen number; α is the slip correction coefficient; S0 is the nominal pumping speed of the pump; β is the transition flow correction coefficient; f(Re) is the correction function related to the Reynolds number.

[0034] Preferably, the effective pumping speed model further includes:

[0035]

[0036] Δp=p 真空腔 -p 泵入口 =p c -p in

[0037]

[0038] In the formula, p in is the pump inlet pressure; p c is the internal air pressure value of the partition; S is the pumping speed; S eff is the effective pumping speed; is the volume flow rate value at the pump inlet.

[0039] According to an embodiment of the second aspect of the present invention, there is provided a method for designing a mass spectrometer vacuum system, comprising the following steps:

[0040] Obtain the vacuum degree requirement value of each partition in the pump model database and the mass spectrometer vacuum system;

[0041] According to the above-mentioned gas flow behavior modeling method, a gas flow behavior model in the mass spectrometer vacuum system is obtained;

[0042] The pumps for each partition in the mass spectrometer are selected according to the vacuum degree requirement value and the gas flow behavior model.

[0043] Preferably, the step of selecting a pump in the mass spectrometer according to the pump model database, the vacuum degree requirement value and the gas flow behavior model specifically includes:

[0044] According to the vacuum degree requirement value of the target partition, a pump that meets the first preset condition is selected from the pump model database;

[0045] According to the gas flow behavior model, an effective pumping speed of the pump is obtained;

[0046] According to the effective pumping speed of the pump, a pump that meets the second preset condition is selected from the pumps that meet the first preset condition, that is, the target pump model is obtained;

[0047] Repeat the above steps until the pumps for all zones are selected.

[0048] Preferably, the first preset condition is: the maximum vacuum degree of the pump is less than or equal to the utilization rate of the pump multiplied by the vacuum degree requirement value, or the pump has a minimum residual pressure;

[0049] The second preset condition is that the rated pumping speed of the pump is greater than or equal to the effective pumping speed.

[0050] According to an embodiment of the third aspect of the present invention, a device for modeling gas flow behavior in a mass spectrometer vacuum system is provided, comprising: a first acquisition unit, a first modeling unit, a second modeling unit and a first processing unit; the first acquisition unit is used to acquire partition information of multiple partitions in the vacuum system of the mass spectrometer; the first modeling unit is electrically connected to the first acquisition unit, and is used to establish a gas flow model for each partition according to the partition information; the second modeling unit is electrically connected to the first acquisition unit and the first modeling unit, and is used to establish an effective pumping speed model for each partition according to the partition information and the gas flow model of each partition; the first processing unit is electrically connected to the second modeling unit, and is used to combine the effective pumping speed models of each partition to obtain a gas flow behavior model in the vacuum system of the mass spectrometer.

[0051] Preferably, the first processing unit includes an analysis module and an execution module, the analysis module is used to analyze the airflow state in each partition according to the gas characteristic parameters and geometric parameters in the partition information, and the execution module is used to establish a gas flow state analysis model for each partition according to the airflow state in each partition.

[0052] According to an embodiment of a fourth aspect of the present invention, a system for designing a mass spectrometer vacuum system is provided, comprising: a second acquisition unit, a second processing unit and a device for modeling gas flow behavior in the above-mentioned mass spectrometer vacuum system; the second acquisition unit is used to acquire a pump model database and vacuum degree requirement values ​​of each partition in the mass spectrometer vacuum system; the device for modeling gas flow behavior in the mass spectrometer vacuum system is used to establish a gas flow behavior model in the mass spectrometer vacuum system; the second processing unit is electrically connected to the second acquisition unit and the device for modeling gas flow behavior in the mass spectrometer vacuum system, respectively, and is used to select pumps for each partition in the mass spectrometer according to the pump model database, the vacuum degree requirement values ​​and the gas flow behavior model.

[0053] According to an embodiment of the fifth aspect of the present invention, there is provided a mass spectrometer vacuum system, comprising: an ion source region, an analysis region, a detector region, an oil-free rotary vane vacuum pump, a turbomolecular pump and an ion sputtering pump; the ion source region, the analysis region and the detector region are connected in sequence, the oil-free rotary vane vacuum pump and the turbomolecular pump are both connected to the ion source region, and the ion sputtering pump is connected to the analysis region; wherein the oil-free rotary vane vacuum pump, the turbomolecular pump and the ion sputtering pump are selected and obtained using the above-mentioned design method for the mass spectrometer vacuum system.

[0054] The gas flow behavior modeling method of the present invention is used to model the gas flow behavior of the mass spectrometer vacuum system. By describing the gas flow state of each partition in the vacuum system respectively, the gas flow state model of each partition is established. This local modeling method can take into account the flow state characteristic differences between the partitions; then, by establishing an effective pumping speed model, the influence of different partitions on the overall vacuum system performance can be effectively analyzed. Finally, the gas flow state model and the effective pumping speed model of each partition are combined to describe the gas flow behavior in the entire vacuum system. The gas flow behavior model established based on this method can simulate and evaluate the gas behavior inside the vacuum system, summarize the behavior of the gas in the vacuum system, especially the flow of the transition area between pumps, optimize the calculation of the gas flow behavior related parameters between the partitions, and provide a design reference for the design of the mass spectrometer vacuum system, especially the selection of the pump. Therefore, this method can accurately model the gas flow behavior of the pipeline of the vacuum system of the mass spectrometer. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 is a schematic diagram of the structure of a mass spectrometer vacuum system in some embodiments of the present invention;

[0056] Figure 2 is a schematic diagram of the structure of a vacuum isolation valve in some embodiments of the present invention;

[0057] Figure 3 is a schematic diagram of a sealing structure between a detector cavity and a cavity cover in some embodiments of the present invention;

[0058] Figure 4 is a schematic diagram of a gas flow path model in some embodiments of the present invention.

[0059] In the figure: 1-oil-free rotary vane vacuum pump, 2-turbomolecular pump, 3-ion sputtering pump, 4-vacuum isolation valve, 5-vacuum sensor, 6-sealing flange, 7-seal, 8-vacuum chamber, 9-sliding valve connecting rod, 10-sliding valve bellows, 11-guide sleeve, 12-ion source, 13-magnetic field mass analyzer, 14-detector system, 15-detector chamber, 16-detector chamber cover, 17-sealing rubber ring. DETAILED DESCRIPTION

[0060] The following will be combined with the accompanying drawings in the present invention to clearly and completely describe the technical solutions in the invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of the present invention.

[0061] In the description of the present invention, it should be noted that the terms "upper", "lower", "upstream", "downstream" and the like indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings and are only for the convenience and simplification of the description. They do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they should not be understood as limitations on the present invention.

[0062] In the description of the present invention, the terms “first”, “second” and “third” are used for descriptive purposes only and should not be understood as indicating or implying relative importance.

[0063] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connect", "set", "install", "fix" and the like should be understood in a broad sense, for example, it can be a fixed connection or a detachable connection, or an integral connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be the internal communication of two elements. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0064] First of all, it should be noted that thermal ionization mass spectrometry has the advantages of high sensitivity, high selectivity, high resolution, adaptability, traceability, and a wide range of element coverage, which makes it widely used in the field of nuclear fuel reprocessing analysis technology. Thermal ionization mass spectrometry has quite superior performance in specific analysis work such as radioisotope analysis, nuclear waste management, nuclear fuel cycle analysis, nuclear fuel quality control, and radioactive waste management.

[0065] Generally, a thermal ionization mass spectrometer (TIMS) is mainly composed of an ion source 12, a magnetic field mass analyzer 13, a detector system 14, a vacuum system, a measurement and control system, and a software system. Among them, the vacuum system is a key part of a thermal ionization mass spectrometer. A high vacuum environment is the basis for the operation of a thermal ionization mass spectrometer. A good vacuum system can create a long mean free path and a chemically clean environment for ions, avoiding ion optical contamination and signal loss caused by collisions between charged ions and background gases and various lenses.

[0066] In order to facilitate understanding of the content of the present invention, the structure of the thermal ionization mass spectrometer is first described: the vacuum system of the thermal ionization mass spectrometer includes an ion source 12, a magnetic field mass analyzer 13 and a vacuum chamber of a detector system 14. Among them, a chamber (called an ionization region) is provided inside the ion source 12. In the ionization region, the sample is coated on the surface of a high melting point metal belt and loaded into the ion source. Under a vacuum state, the sample is heated and evaporated by adjusting the current intensity flowing through the metal belt, and some neutral particles are ionized to form ions during the evaporation process. A curved channel is provided inside the magnetic field mass analyzer 13, and a magnetic field exists in the curved channel. The ionization region is connected to the curved channel, and the charged ions generated in the ionization region are accelerated into the curved channel. The magnetic field inside the curved channel causes the charged ions to be subjected to the Lorentz force. Due to the different mass and charge ratios of different charged ions, under the influence of the Lorentz force, different charged ions will have different movement paths, which will lead to different degrees of deflection of the ions in the magnetic field, thereby achieving mass separation. A receiving cavity (i.e., detector cavity 15) is provided inside the detector system 14, and the receiving cavity (i.e., detector cavity 15) is connected to one end of the curved channel relative to the ionization region, and is used to capture ions passing through the analysis region and convert them into measurable signals.

[0067] In other words, the mass spectrometer has multiple partitions, namely: ion source area, analysis area and detector area, and the ion source area, analysis area and detector area are connected in sequence. Figure 1 More specifically, the ion source region is the ionization region inside the ion source 12; the analysis region is the curved channel inside the magnetic field mass analyzer 13; and the detector region is the receiving cavity (ie, the detector cavity 15) inside the detector system 14.

[0068] The vacuum system of the mass spectrometer also includes: an oil-free rotary vane vacuum pump 1, a turbomolecular pump 2 and an ion sputtering pump 3, wherein the oil-free rotary vane vacuum pump 1 and the turbomolecular pump 2 are both connected to the ion source area, and the oil-free rotary vane vacuum pump 1 is used for pre-vacuuming in the injection system. The turbomolecular pump 2 is used to keep the ion source 12 at a high vacuum and is used for vacuum pre-evacuation after the analysis chamber is vented. The ion sputtering pump 3 is used to ensure that the analysis area reaches an ultra-high vacuum.

[0069] It is easy to understand that mass spectrometry needs to be performed under high vacuum conditions because gas molecules interfere with the generation and transmission of ions. By reducing the gas pressure, the number of gas molecules can be reduced, thereby increasing the free path of ions and avoiding their collision with the gas. However, the vacuum requirements of different partitions in the vacuum system of the mass spectrometer are not the same, which leads to a very complex gas flow pattern.

[0070] When designing the vacuum system of current mass spectrometers, there is a lack of accurate modeling and calculation of the complex flow patterns of gases in the vacuum pipeline, especially in the transition area between pumps. After the pump responsible for vacuum extraction is installed, it is often impossible to obtain the ideal gradient vacuum or the extraction speed is slow. Therefore, mass spectrometers designed by some manufacturers at home and abroad often need to be readjusted or changed after installation to deal with performance problems caused by the inaccurate design of the vacuum system. This phenomenon can be traced back to the fact that the complexity of the vacuum system was not fully considered during the design stage. The lack of detailed gas flow model calculations may lead to improper selection of parameters such as the position, layout and pipe diameter of the pump in the vacuum system, thereby affecting the overall performance of the system.

[0071] In summary, the quality of the vacuum system plays a decisive role in ionization efficiency, ion transmission, background noise, instrument stability, etc. In order to improve the design accuracy of the vacuum system, a more sophisticated gas flow dynamics analysis must be introduced in the early stage of the design to ensure that the gas flow behavior between the components is reasonably optimized. Such an approach can not only reduce the need for subsequent adjustments, but also help promote the continuous advancement of mass spectrometer technology.

[0072] Example 1

[0073] See also Figure 1 The present invention discloses a method for modeling gas flow behavior in a vacuum system of a mass spectrometer. The vacuum system of the mass spectrometer has multiple partitions, and the multiple partitions are connected in sequence. The method comprises the following steps:

[0074] obtaining partition information of a plurality of partitions in a vacuum system of a mass spectrometer;

[0075] According to the partition information, the gas flow model of each partition is established respectively;

[0076] According to the partition information and the gas flow model of each partition, the effective pumping speed model of each partition is established respectively;

[0077] The effective pumping speed models of each partition are combined to obtain the gas flow behavior model in the mass spectrometer vacuum system.

[0078] It should be noted that the method in this embodiment can be executed using a software module. This method can more accurately describe the gas flow behavior of each partition by independently modeling each partition in the mass spectrometer vacuum system. This local modeling method can take into account the differences in flow characteristics between the partitions and improve the reliability of the overall model. Then, by establishing an effective pumping speed model, the impact of different partitions on the overall vacuum system performance can be effectively analyzed.

[0079] Specifically, the pumping speed refers to the amount of gas that the vacuum pump can pump out per unit time. The pumping speed is directly related to the gas flow and pressure distribution of the vacuum system. Through the pumping speed of each partition, the role of each partition in the overall vacuum system and its impact on the system performance can be quantitatively analyzed. The change in pumping speed reflects the actual operating status of each partition. Furthermore, there is gas flow resistance during the gas flow process. Due to the gas flow resistance behavior, the effective pumping speed of the pump is usually not equal to the actual pumping speed. Therefore, this method also takes the gas flow resistance behavior into account and establishes an effective pumping speed model. In the process of simulating gas movement, for complex mass spectrometers, the relationship between gas flow and flow resistance can be equivalent to the relationship between current and resistance. According to the connection method between the pipelines, the flow resistance can be calculated similarly to the series and parallel connection of resistors.

[0080] By analyzing the gas flow pattern and effective pumping speed of each partition and then combining their equations, the overall gas flow behavior model of the system is obtained, which is convenient for describing the complex gas flow behavior in the pipeline of the vacuum system and also provides an effective basis for the subsequent design of the vacuum system.

[0081] In summary, the modeling method of the gas flow behavior in the vacuum system of the mass spectrometer can accurately model the gas flow in the pipeline of the vacuum system of the mass spectrometer.

[0082] Specifically, the partition information includes gas characteristic parameters, geometric parameters and pumping speed characteristic parameters; gas characteristic parameters include: gas viscosity η, gas density ρ, gas flow rate v, gas pressure value p; geometric parameters include: partition pipe cross-section equivalent diameter d; pumping speed characteristic parameters include: pump inlet pressure value, partition internal pressure value, pump inlet volume flow value and leakage rate in the partition. All the above parameters can be obtained through actual measurement.

[0083] Furthermore, in this embodiment, the above step of establishing the gas flow model of each partition according to the partition information includes:

[0084] According to the gas characteristic parameters and geometric parameters in the partition information, the airflow state in each partition is analyzed. It should be noted that in the step of analyzing the airflow state in each partition, existing simulation software can be used. Specifically, a finite element model is established according to the gas characteristic parameters and geometric parameters, such as Figure 4 As shown, the airflow state of each partition is obtained by solving it through simulation software (such as moflow, FLUNET, etc.).

[0085] Then, according to the airflow state in each partition, the gas flow model of each partition is established. Generally, the flow state of gas can be divided into turbulent flow, viscous flow, molecular flow and the transition state between them (i.e. the transition state between viscous flow and molecular flow, or called Knudsen flow).

[0086] Specifically, the airflow state in each partition is judged to be the first flow state or the second flow state in turn:

[0087] When the air flow state in the partition is the first flow state, the gas flow state model adopts the Reynolds number expression, and the first flow state is a turbulent state.

[0088] When the gas flow state in the partition is the second flow state, the gas flow state model adopts the Knudsen number expression, and the second flow state is viscous flow, molecular flow or transitional flow state.

[0089] The Reynolds number expression is:

[0090]

[0091] Where Re is the Reynolds number, η is the gas viscosity, ρ is the gas density, v is the gas velocity, and d is the equivalent diameter of the pipe cross section. When Re>4000, it is turbulent flow; when Re<2300, it is viscous flow.

[0092] The Knudsen number expression is:

[0093]

[0094] Where Kn is the Knudsen number; v is the gas velocity; η is the gas viscosity; p is the gas pressure; d is the equivalent diameter of the partitioned pipe cross section. When Kn>0.5, it is molecular flow; when Kn<0.01, it is viscous flow; when 0.01<Kn<0.5, it is transition state.

[0095] Specifically, in the simulation software, the initial flow state of the gas in the partition can be regarded as a turbulent state. Then, the gas viscosity η, gas density ρ, gas flow rate v, gas pressure value p, and the equivalent diameter d of the partition pipe cross section and other related parameters are substituted into the Reynolds number expression, and the flow state of the Reynolds number is judged according to the calculated results. When Re>4000, the airflow state in the target partition can be judged as the first flow state (turbulent); when Re<4000, the airflow state in the target partition can be judged as the second flow state (molecular flow, viscous flow and transitional flow state). Then, by calculating the Knudsen number, the airflow in the second flow state in the partition can be specifically distinguished as molecular flow, viscous flow or transitional flow state.

[0096] For the gas flow in the first flow state, the Reynolds number expression is used to establish the gas flow model; for the gas flow in the second flow state, the Knudsen number expression is used to establish the gas flow model. The advantage of this is that the gas flow model is established through parameters such as gas viscosity η, gas density ρ, gas flow rate v, gas pressure value p, and partitioned pipe cross-section equivalent diameter d, which can be more accurately classified in microscale or low-pressure environments, and can be well combined with the physical property changes of different gases, and is suitable for dynamic models.

[0097] Effective pumping speed models include:

[0098] Q=P·S eff ·F(Kn)

[0099] F(Kn)=1+α·Kn

[0100] S eff =S0·(1-β·f(Re))

[0101] Q=P·S0·(1-β·f(Re))·(1+α·Kn)

[0102] Where Q is the leakage rate in the partition; P is the pressure in the system; S eff is the effective pumping speed; F(Kn) is the correction term dependent on the Knudsen number; α is the slip correction coefficient; S0 is the nominal pumping speed of the pump; β is the transition flow correction coefficient; f(Re) is the correction function related to the Reynolds number.

[0103] Specifically, the simulation of the vacuum system of a mass spectrometer involves several key factors, including leak rate, effective pumping speed, gas flow model, and flow regime transition (such as from turbulent flow to molecular flow).

[0104] Leakage rate (Q) and effective pumping speed (S eff The relationship between the leak rate and the pumping speed is the core issue in the simulation of the mass spectrometer vacuum system. The leak rate represents the rate at which gas enters the system, while the pumping speed represents the system's ability to remove gas. The balance between the two determines the vacuum degree of the system:

[0105] Q = P·S eff

[0106] Where:

[0107] Q is the leak rate, P is the pressure inside the system, and S eff is the effective pumping speed. Here, P is the统称 of the internal air pressure values p of each partition c .

[0108] In this embodiment, a model applicable to a mass spectrometer that combines a gas flow model is proposed. This model is applicable to the simulation of the gas transition state:

[0109] (1) Relationship between the Knudsen number and the leak rate

[0110] Under transitional flow and slip flow conditions (0.01 < Kn < 10), the relationship between the leak rate and the pressure of the system is no longer linear, and the slip effect of the gas and the transitional characteristics of molecular motion need to be considered. The leak rate formula is improved by introducing the Knudsen extended model.

[0111] In a high-vacuum system, as the Knudsen number increases, the gas transitions from continuous flow to molecular flow, and the leak rate model must consider this transition process. By introducing the Knudsen number correction term F(Kn), the new leak rate formula can be expressed as:

[0112] Q = P·S eff ·F(Kn)

[0113] Where F(Kn) is a correction term that depends on the Knudsen number and reflects the change in the leak rate under different flow states. It can be defined as:

[0114] F(Kn) = 1 + α·Kn

[0115] α is the slip correction coefficient; when Kn → 0, F(Kn) ≈ 1, indicating the leak rate in continuous flow; when Kn → ∞, F(Kn) increases, indicating that the leak rate effect in rarefied gas flow gradually increases.

[0116] The correction of F(Kn) here means quantifying the influence of the leak rate on the gas system in the cavity. Specifically, when the Knudsen number approaches 0, the gas is continuous and sufficient. If there is a leak point at this time, when calculating the effective pumping speed S eff , that is to say, an effective pumping speed can be directly corresponding to the leak rate, and the gas leaking into the system can be easily pumped away directly by the pump. When Kn → ∞, F(Kn) increases, indicating that the leak rate of the rarefied gas flow has a very large impact on the gas. When calculating the effective pumping speed, it shows that the gas molecules leaking into the system are difficult to be directly pumped away by the pump under this condition.

[0117] In the second flow state, when Kn>0.5, it is molecular flow, when Kn<0.01, it is viscous flow, and when 0.01<Kn<0.5, it is a transition state. That is to say, from viscous flow to molecular flow, the influence of the Knudsen number correction coefficient becomes increasingly greater.

[0118] The correction coefficients α and β here are usually estimated using DSMC (Direct Simulation Monte Carlo Method) or CFD (Computational Fluid Dynamics), and sometimes they are determined using empirical formulas or experiments. Since this coefficient usually only needs to be roughly estimated, it will not be described in detail here.

[0119] (2) Relationship between Reynolds number and pumping speed

[0120] The Reynolds number is used to describe the flow pattern of gas in the pipeline, and mainly affects the effective pumping speed of the gas. According to different Reynolds number ranges, the effective pumping speed of the system can be modified as follows:

[0121] S eff =S0·(1-β·f(Re))

[0122] in:

[0123] S0 is the nominal pumping speed of the pump; β is the transition flow correction factor; f(Re) is a correction function related to the Reynolds number, which can be determined based on experiments or numerical simulations.

[0124] When the mass spectrometer starts to evacuate from atmospheric conditions, f(Re) = 0; after the gas is gradually pumped away by the pump, the gas flow rate decreases, the viscosity effect increases, the pumping speed decreases, and f(Re) gradually increases.

[0125] (3) Comprehensive model combining Knudsen number and Reynolds number

[0126] By combining the Knudsen number with the Reynolds number, a more comprehensive leak rate-pumping speed model can be obtained:

[0127] Q=P·S0·(1-β·f(Re))·(1+α·Kn)

[0128] The correction coefficients in this model can be determined based on experiments or numerical simulations. For large mass spectrometers or more complex mass spectrometer vacuum systems, the parameters in this model are usually first calculated using experimental measurement methods, component-level simulation methods, experimental-simulation combined methods, and other methods, and then the entire vacuum system is simulated as a whole.

[0129] Furthermore, the effective pumping speed model also includes:

[0130]

[0131] Δp=p 真空腔 -p 泵入口 =pc -p in

[0132]

[0133] In the formula, p in is the pump inlet pressure; p c is the internal air pressure value of the partition; S is the pumping speed; S eff is the effective pumping speed; is the volume flow rate value at the pump inlet.

[0134] The pressure difference Δp is intended to indicate that when simulating the setting of the pumping speed (i.e., the selection of the pumping position), the selection of the pumping speed must satisfy the pressure difference Δp = p 真空腔 -p 泵入口 >0 or higher than a certain threshold value, so that the gas can overcome the flow resistance and be finally pumped out from the cavity to the pump.

[0135] In this application, the inflow of gas is directly based on To calculate the effective pumping speed, and to reflect the dynamic behavior of the gas through the pressure difference, it emphasizes the flow characteristics of the gas in the system and is suitable for more complex flow conditions. In other words, the pumping speed calculation model proposed in this application is more suitable for calculating the effective pumping speed under complex conditions.

[0136] It should be noted that the effective pumping speed model here refers to the pump. The focus here is on how to push it down to the volume flow value of the pump after completing the evaluation of the gas in the cavity. These formulas will be used in addition in actual design to calculate the volume and pressure requirements in the simulated pump. At the same time, since the simulation software can only view the cavity pressure value, surface pressure value, and cross-sectional pressure value during the program simulation process, this part of the model is used for inspection or adjustment. In addition, when the material leakage rate measurement experiment is not performed, this part of the model is usually used for simulation calculation to estimate the modeling of the required pump. If sufficient condition parameters are obtained, it is possible to use only the above pumping speed model.

[0137] In summary, this application proposes a modeling method for gas flow behavior in a mass spectrometer vacuum system, which can be applied to the design and implementation of a vacuum system for a thermal ionization mass spectrometer, and is particularly suitable for describing the complex flow state of gas in a vacuum system. This method can help optimize the realization of gradient vacuum and improve the vacuum extraction speed.

[0138] In other words, this method simulates and evaluates the gas behavior inside the vacuum system, summarizes the behavior of gas in the vacuum system, especially the flow conditions in the transition area between pumps, optimizes the calculation of gas flow resistance between pipelines and between pipelines and pumps, and provides a certain design reference for the vacuum systems of other mass spectrometers.

[0139] Example 2

[0140] See also Figure 1 The present invention also discloses a method for designing a mass spectrometer vacuum system, comprising the following steps:

[0141] Obtain the vacuum degree requirement value of each partition in the pump model database and the mass spectrometer vacuum system;

[0142] According to the gas flow behavior modeling method in Example 1, a gas flow behavior model in the mass spectrometer vacuum system is obtained;

[0143] The pumps for each partition in the mass spectrometer are selected based on the pump model database, vacuum requirement value and gas flow behavior model.

[0144] It should be noted that the pump model database can be a database constructed by staff based on the existing pump equipment on the market, which includes the pump model and the maximum vacuum degree, minimum residual pressure, pump utilization rate and rated pumping speed corresponding to each model.

[0145] Specifically, in the vacuum system of the thermal ionization mass spectrometer, the partitions include the ion source area, the analysis area, and the detector area. The ion source 12 and the ion lens area (i.e., the ion source area) require high vacuum, and the vacuum degree requirement value is usually 10 -6 Up to 10 -9 The ion source area has some specific requirements for vacuum, such as fast vacuum pumping and recovery speed, stability, sufficient vacuum monitoring, etc. In addition, the vacuum requirement value of the analysis area and the detector area is usually 10 -8 Up to 10 -10 mbar, which belongs to the ultra-high vacuum range. For further example, the vacuum degree requirement of the ion source area of ​​the vacuum system is 2×10 -8 mbar; the vacuum requirement for the analysis area is 7×10 -9 mbar, the vacuum requirement of the detector area is 2×10 -9 .

[0146] Then, based on the pump model database, vacuum requirement value and gas flow behavior model, the pumps for each partition in the mass spectrometer are selected, including:

[0147] According to the vacuum degree requirement value of the target partition, a pump that meets the first preset condition is selected from the pump model database;

[0148] According to the gas flow behavior model, the effective pumping speed of the pump is obtained;

[0149] According to the effective pumping speed of the pump, the pump that meets the second preset condition is selected from the pumps that meet the first preset condition, and the target pump model is obtained. Repeat the above steps until the pumps for all partitions are selected.

[0150] Specifically, the first preset condition is that the maximum vacuum degree of the pump is less than or equal to the utilization rate of the pump multiplied by the vacuum parameter of the pump, or the pump has a minimum residual pressure. The second preset condition is that the rated pumping speed of the pump is greater than or equal to the effective pumping speed.

[0151] In other words, this vacuum system should meet two conditions when selecting a pump:

[0152] 1) The first pre-condition is:

[0153] P max ≤K×P

[0154] Among them, P max is the maximum vacuum of the pump; K is the utilization rate of the pump; P is the required vacuum of the pump (i.e. the required vacuum of the partition). K is generally not more than 0.5. If this condition is not met, a pump with the minimum residual pressure must be selected.

[0155] It should be noted that the maximum vacuum degree of the pump P max In fact, it refers to the lowest air pressure value that the partition can reach during the operation of the pump; the vacuum requirement value P is the lowest air pressure value that the partition is required to reach; in other words, the greater the vacuum, the lower the air pressure value. The pump utilization rate K is a parameter less than 0.5, so K is used as a coefficient of the vacuum requirement value P. The value range of the pump utilization rate K can be 0.1-0.4, for example: 0.1, 0.2, 0.3 or 0.4.

[0156] 2) The second preset condition is:

[0157] S R ≥S

[0158] That is, the rated pumping speed of the selected vacuum pump must be greater than or equal to the calculated vacuum pumping speed. R is the rated pumping speed of the pump, and S is the effective pumping speed of the pump.

[0159] Taking the analysis area as an example, the pump selection steps are explained: The vacuum requirement value of the analysis area is 10 -8 , K is 0.4. At this time, the maximum vacuum degree of the pump is required to be less than or equal to 4×10 -9 . Filter all pump models with a maximum vacuum of 4×10 -9Then, from the pump models that meet the first preset condition, the pump model with a rated pumping speed greater than the effective pumping speed is selected, which is the target pump model, thereby completing the selection of the pump for the analysis area. The selection process of the pumps for the ion source area and the detector area is similar and will not be repeated here.

[0160] In summary, the design method of the mass spectrometer vacuum system in this embodiment studies the performance influencing factors of each component in the vacuum system, such as the type, layout, and number of pumps, based on the simulation of gas flow behavior, and uses more efficient and compact vacuum pump technology to optimize the realization of gradient vacuum and improve the vacuum extraction speed and stability.

[0161] Example 3

[0162] In this embodiment, a specific example of a design method for a mass spectrometer vacuum system is provided.

[0163] In the process of designing the vacuum system of the mass spectrometer, the flow pattern of the gas in the vacuum pipeline is first summarized and modeled.

[0164] The following is a detailed description of the simulation process of the gas molecule motion behavior and pump selection in this vacuum system:

[0165] The design process of the vacuum system of this spectrometer can be realized by using existing simulation software (such as moflow, FLUNET and other fluid simulation software).

[0166] 1. According to the actual design of thermal ionization mass spectrometer, establish a high-precision three-dimensional model and a gas flow model, such as Figure 4 That is, a geometric model of the vacuum system of the thermal ionization mass spectrometer is established, and the geometric model is imported into the simulation software.

[0167] 2. In the gas molecule motion behavior simulation software, set relevant parameters (i.e., initial solution parameters), including: the position of the pump (i.e., the initial setting position of the pump), the pumping speed of the pump (i.e., the initial setting pumping speed of the pump), the gas leakage rate at each flange port, the desorption parameters of the material, etc. At the same time, the gas flow behavior model established in Example 1 is called by the simulation software. The description of the gas flow behavior model is as follows:

[0168] The vacuum chamber 8 of the thermal ionization mass spectrometer has different vacuum requirements according to its function. Therefore, the type, number and layout of the pumps should ensure that the mass spectrometer as a whole maintains a gradient stable vacuum environment. The ion source 12 and ion lens area require high vacuum, usually at 10 -6 Up to 10 -9 mbar. The ion source area has some specific requirements for vacuum, such as fast vacuum pumping and recovery speed, stability, and sufficient vacuum monitoring. The vacuum degree of the analysis area and the detector area is usually 10-7 Up to 10 - 9 mbar, which belongs to the ultra-high vacuum range.

[0169] Furthermore, when selecting the location of the pump for this vacuum system, it is necessary to simulate and evaluate the gas behavior inside the vacuum system. Generally, the flow state of gas can be divided into turbulent flow, viscous flow, molecular flow and the transitional flow state between them. In the turbulent state, friction (gas viscosity η), mass inertia (proportional to gas density ρ), flow velocity v, and cross section d are used for evaluation. The evaluation formula is as follows:

[0170]

[0171] Among them, Re is the Reynolds number. When Re>4000, it is turbulent flow; when Re<2300, it is viscous flow.

[0172] Viscous flow, molecular flow and their transition states are simulated and calculated using the Knudsen number, which is expressed as follows:

[0173]

[0174] Where p is the pressure, Kn is the Knudsen number, when Kn>0.5 it is molecular flow, when Kn<0.01 it is viscous flow, and when 0.01<Kn<0.5 it is a transition state.

[0175] Furthermore, when the vacuum container is evacuated by the vacuum pump, the volume of gas flowing through the pump inlet per unit time (the volume flow rate at the pump inlet) is the pumping speed S of the pump. The expression of the pumping speed is:

[0176]

[0177] Among them, S is the pumping speed, which is usually expressed in volume units (such as cubic meters per second), indicating the volume of gas flowing into the system per unit time. is the volume flow rate of the gas inlet, which means the volume of gas passing through the inlet per unit time.

[0178] During the vacuuming process, the gas flows out of the chamber, through the pipe, and to the pump, requiring a pressure difference, which is expressed as follows:

[0179] Δp=p 真空腔 -p 泵入口 =p c -p in

[0180] There is gas flow resistance in the flow process. Due to the gas flow resistance behavior, the effective pumping speed of the pump is usually not equal to S, that is, S needs to be multiplied by a correction factor. The expression of the effective pumping speed of the pump is as follows:

[0181]

[0182] In the process of simulating gas movement, for complex mass spectrometers, the relationship between gas flow and flow resistance can be equivalent to the relationship between current and resistance. According to the connection method between pipelines, the flow resistance can be calculated similarly to the series and parallel connection of resistors.

[0183] It should also be noted that during the simulation process, it is sometimes necessary to define the flow resistance of a partial volume or wall. In other words, during the simulation process, it is sometimes necessary to define the wall friction so that the software can calculate the gas flow resistance.

[0184] 1. Darcy-Weisbach equation

[0185] This equation is used to calculate the pressure loss (ΔP) in a pipe:

[0186]

[0187] in:

[0188] ΔP is the pressure loss (Pa);

[0189] f is the Darcy friction factor, which depends on the Reynolds number (Re) and the relative roughness of the pipe;

[0190] L is the length of the pipeline (m);

[0191] D is the inner diameter of the pipe (m);

[0192] ρ is the density of the gas (kg / m3);

[0193] v is the flow velocity of the gas (m / s).

[0194] 2. Calculation of Darcy friction factor f

[0195] The calculation of the friction factor depends on the type of flow:

[0196] In laminar flow (when Reynolds number Re < 2000), the friction factor f can be directly calculated by the following formula:

[0197]

[0198] In turbulent flow (Re>4000), the friction factor f can be calculated by the Colebrook-White equation, or the approximate Swamee-Jain equation, which is related to the pipe roughness and the Reynolds number.

[0199] The Swamee-Jain equation is a commonly used approximate formula:

[0200]

[0201] in:

[0202] ∈ is the roughness of the inner wall of the pipe (m). For stainless steel pipes, the roughness is usually around 0.0015mm.

[0203] 3. Select the mass spectrometer wall where the pressure needs to be observed or create a cross section in the model to calculate the flux, set the meshing method according to the finite element method, and set the pressure observation direction of the cross section.

[0204] 4. Run the simulation software. The simulation software solves the gas flow behavior model according to the above solution parameters, obtains and records the real-time wall pressure heat map, cross-sectional pressure curve, and the movement behavior of gas molecules inside the model.

[0205] 5. Set the pressure threshold for stopping the simulation, record the time from the start of the simulation to the end of the simulation, and evaluate the stability, effectiveness, and responsiveness of the vacuum system of the model.

[0206] At this point, the initial solution calculation process is completed, and the next iterative calculation is performed based on the relevant parameters obtained by the solution.

[0207] 6. The subsequent iterative calculation process is as follows: First, adjust the position of the pump in the model and reselect the pump (i.e. adjust the pumping speed and other parameters), and then substitute it into the simulation software for calculation to obtain the iterative real-time wall pressure heat map, cross-sectional pressure curve, and gas molecule motion behavior inside the model. Observe the trend of the heat map and curve changes, compare the time from the start of the simulation to the end of the simulation, analyze the differences in the vacuum system under different models, and select the optimal model solution.

[0208] Furthermore, the vacuum system should meet two conditions when selecting the pump:

[0209] 1) The first pre-condition is:

[0210] P max ≤K×P

[0211] Among them, P max is the maximum vacuum of the pump; K is the utilization rate of the pump; P is the actual vacuum required by the pump. K is generally selected not to exceed 0.5. If this condition is not met, a pump with minimum residual pressure must be selected.

[0212] 2) The second preset condition is:

[0213] S R ≥S

[0214] In other words, the rated pumping speed of the selected vacuum pump must be greater than or equal to the calculated vacuum pumping speed.

[0215] Example 4

[0216] The present invention also discloses a modeling device for gas flow behavior in a vacuum system of a mass spectrometer, comprising: a first acquisition unit, a first modeling unit, a second modeling unit and a model unit.

[0217] The first acquisition unit is used to acquire the partition information of multiple partitions in the vacuum system of the mass spectrometer. The first processing unit is electrically connected to the first acquisition unit and is used to establish the gas flow state model of each partition according to the partition information. The second modeling unit is electrically connected to the first acquisition unit and the first modeling unit respectively and is used to establish the effective pumping speed model of each partition according to the partition information and the gas flow state model of each partition. The first processing unit is electrically connected to the second modeling unit and is used to combine the effective pumping speed models of each partition to obtain the gas flow behavior model in the vacuum system of the mass spectrometer.

[0218] It should be noted that the device is used to execute the modeling method of gas flow behavior in the vacuum system of the mass spectrometer in Example 1. The device can be implemented using a software module. The first acquisition unit can be a database module. After the staff obtains the partition information of multiple partitions in the vacuum system, the partition information of the multiple partitions is uploaded to the database. The first modeling unit is electrically connected to the first acquisition unit and can call the partition information in the database.

[0219] Specifically, the second modeling unit includes an analysis module and an execution module. The analysis module is used to analyze the airflow state in each partition according to the gas characteristic parameters and geometric parameters in the partition information, and the execution module is used to establish the gas flow state model of each partition according to the airflow state in each partition.

[0220] In summary, this modeling device can simulate and evaluate the gas behavior inside the vacuum system, summarize the behavior of the gas in the vacuum system, especially the flow conditions in the transition area between pumps, optimize the calculation of the gas flow resistance between pipelines and between pipelines and pumps, and provide a certain design reference for the design of the vacuum system of the mass spectrometer.

[0221] Example 5

[0222] The present invention also discloses a design system for a mass spectrometer vacuum system, comprising: a second acquisition unit, a second processing unit and a modeling device for gas flow behavior in the mass spectrometer vacuum system in Example 4.

[0223] The second acquisition unit is used to obtain the vacuum degree requirement values ​​of each partition in the vacuum system of the mass spectrometer from the pump model database. The modeling device is used to establish a gas flow behavior model in the vacuum system of the mass spectrometer, specifically, to obtain the gas flow behavior model in the vacuum system of the mass spectrometer according to the gas flow behavior modeling method in Example 1. The second processing unit is electrically connected to the second acquisition unit and the modeling device, respectively, and is used to select the pumps for each partition in the mass spectrometer according to the pump model database, the vacuum degree requirement value and the gas flow behavior model.

[0224] It should be noted that the system is used to implement the design method in the mass spectrometer vacuum system in Example 2. The system can be implemented using a software module. The second acquisition unit can be a database module, which includes a pump model database and a vacuum degree requirement value database. The pump model selected by the staff is uploaded to the database module to form a pump model database. The pump model database also stores the vacuum degree requirement values ​​of each partition. For example: the vacuum degree requirement value of the ion source area is 10 -6 ; The vacuum requirement for the analysis area and detector area is 10 -8 .

[0225] By adopting the modeling device in Example 4 to execute the modeling method of gas flow behavior, the calculation of gas flow resistance between pipelines and between pipelines and pumps is optimized, providing a certain design reference for the design of the vacuum system of the mass spectrometer.

[0226] Then, the second processing unit may be a computer software module for selecting a pump in the mass spectrometer according to the pump model database, the vacuum requirement value and the gas flow behavior model.

[0227] In summary, the design system of the essential spectrometer vacuum system studies the factors affecting the performance of each component in the vacuum system, such as the type, layout, and number of pumps, based on the simulation of gas flow behavior, so as to achieve better pump selection, optimize the realization of gradient vacuum, and improve the vacuum extraction speed and stability.

[0228] Example 6

[0229] The invention also discloses a mass spectrometer vacuum system, comprising: an ion source area, an analysis area, a detector area, an oil-free rotary vane vacuum pump 1, a turbomolecular pump 2 and an ion sputtering pump 3.

[0230] The ion source area, the analysis area and the detector area are connected in sequence, the oil-free vane vacuum pump 1 and the turbomolecular pump 2 are both connected to the ion source area, and the ion sputtering pump 3 is connected to the analysis area. The oil-free vane vacuum pump 1, the turbomolecular pump 2 and the ion sputtering pump 3 are selected and obtained by adopting the design method of the mass spectrometer vacuum system in Example 2.

[0231] Specifically, the vacuum system consists of a vacuum chamber 8, an oil-free rotary vane vacuum pump 1, a turbomolecular pump 2, an ion sputtering pump 3, a vacuum isolation valve 4, a vacuum sensor 5, a sealing flange 6, and a seal 7 (a sealing copper gasket or a sealing silver wire can be used. Usually, the seal of component 7 uses a copper gasket. Using a silver wire seal instead of a copper gasket can obtain a lower leakage rate.).

[0232] The selection and placement of each pump must meet the requirements that the vacuum of the ion source cavity is better than 5×10 -6 Pa(5×10 -8 mbar), the analysis chamber is better than 3×10 -7 Pa(3×10 -9 mbar).

[0233] Specifically, the oil-free rotary vane vacuum pump 1 is used for pre-vacuuming the sample injection system. When the pump is started, the vacuum is usually poor and the gas flow in the vacuum chamber 8 is turbulent. Therefore, the pump needs to be placed at the front end and use a high pumping speed to quickly complete the transition to viscous flow.

[0234] The turbomolecular pump 2 is used to maintain a high vacuum in the sample injection system and the ion source 12, and is used for vacuum pre-pumping after the analysis chamber is emptied. The pump is located near the oil-free rotary vane vacuum pump 1, and the gas flows in a viscous manner. This position can ensure that the probability of airflow collision is reduced, the flow resistance is reduced, and the transition to molecular flow is completed quickly.

[0235] The ion sputtering pump 3 is used to ensure that the analysis area reaches a high vacuum. The device is based on the absorption of gas by the cathode material (titanium) during high-voltage discharge in a magnetic field. The pump is located near the back of the turbomolecular pump 2, and when the cavity is large, multiple pumps can be added in the middle and rear sections according to demand. In the present invention, the motion behavior of the gas molecular flow in the cavity and the vacuum demand are comprehensively calculated and simulated, and two ion sputtering pumps 3 are selected to be located between the vacuum isolation valve and the flight flat tube, and between the flight flat tube and the detector cavity 15.

[0236] The vacuum isolation valve 4 can cut off and isolate the ion source 12 cavity from the high vacuum area of ​​the analysis chamber, thereby ensuring that the high vacuum area of ​​the analysis system is clean and dry during the cleaning, maintenance and sample replacement of the ion source 12.

[0237] Components such as the ion sputtering pump 3 and valves can withstand high-temperature baking treatment at 250°C to 300°C.

[0238] The vacuum sensor 5 is installed on the pump exhaust pipe, the ion source 12 cavity, and the ion flight pipeline. The vacuum sensor 5 connected to the pump exhaust pipe is used to monitor the pre-vacuum pressure in real time, and can determine whether the turbomolecular pump 2 can be turned on. The vacuum sensor 5 connected to the ion source 12 cavity is used to monitor whether the vacuum isolation valve can be opened after sample replacement, and monitor whether the lens high pressure can be opened. The vacuum sensor 5 connected to the ion flight pipeline is used to determine the cleanliness of the ion flight path during the sample measurement process.

[0239] During the vacuuming process of the thermal ionization mass spectrometer after the first assembly, baking measures are taken. A heating belt is used to wrap and bake the outside of the cavity, and the gas desorbed from the surface of the material, the gas diffused from the inside of the material to the surface, and the gas that penetrates into the vacuum through the cavity wall leave the system at high temperature. The oil-free rotary vane vacuum pump 1 and the turbomolecular pump 2 are turned on for vacuuming, and the baking function of the ion sputtering pump 3 is used at the same time.

[0240] The following will further explain the various parts of this vacuum system:

[0241] like Figure 1 As shown, this embodiment provides a vacuum system design and implementation method for a thermal ionization mass spectrometer, including: a vacuum chamber 8, an oil-free rotary vane vacuum pump 1, a turbomolecular pump 2, an ion sputtering pump 3, a vacuum isolation valve 4, a vacuum sensor 5, a sealing flange 6, and a seal 7 (a sealing copper gasket or a sealing silver wire can be used).

[0242] The oil-free rotary vane vacuum pump 1 is used for pre-vacuuming the sample injection system. The selected oil-free rotary vane vacuum pump 1 has a maximum pressure of 0.67Pa and a pumping rate of 200L / min. The turbomolecular pump 2 is used to maintain a high vacuum in the ion source 12 and is used for vacuum pre-pumping after the analysis chamber is emptied. The pumping rate of the turbomolecular pump 2 is 255L / s and the maximum pressure is 1×10 -10 mbar, and the speed is 60000r / min. The ion sputtering pump 3 is used to ensure that the analysis area reaches a high vacuum. The operating speed of the ion sputtering pump 3 is about 160L / s (at 1×10 -6 Pa). The welded shell of the ion sputtering pump 3 is made of stainless steel to form a sealed volume, and the nominal diameter of the air inlet pipe connecting flange is 100 (unit: mm). A connecting pipe is welded to the shell, and the nominal diameter of the flange is 16 (unit: mm), which is used to connect the high-voltage vacuum input end. The anode voltage of the ion sputtering pump 3 can be selected by the user as 3kV, 5kV, or 7kV according to needs. The ion sputtering pump 3 itself can complete baking at ≤300°C. After pre-vacuuming with an oil-free vacuum pump and a turbomolecular pump 2, the ion sputtering pump 3 reaches the start-up condition. At this time, the ion sputtering pump 3 is turned on to absorb the remaining gas inside the pipeline. The ion sputtering pump 3 can ensure that the pressure in the analysis chamber is not greater than 3×10 -7 Pa(3×10-9 mbar).

[0243] like Figure 2 As shown, in this embodiment, the vacuum isolation valve 4 is composed of a slide valve connecting rod 9, a slide valve bellows 10, a guide sleeve 11, a sealing rubber ring 17 and other accessories. It is sealed between the cavity of the ion source 12 of the thermal ionization mass spectrometer and the flight flat tube through a sealing flange 6. It is used to isolate the high vacuum area of ​​the ion source 12 and the ion lens from the ultra-high vacuum area of ​​the analysis and detector.

[0244] The sliding valve connecting rod 9 is used to connect to an external push rod to manipulate the movement of the valve.

[0245] The slide valve bellows 10 is used to provide a flexible seal when the valve moves and allows a certain degree of deformation to adapt to the movement of the valve. The slide valve bellows 10 is usually made of a soft, elastic metal material, such as stainless steel. The slide valve bellows 10 provides an effective seal when the valve is closed to prevent gas leakage. The valve requires a certain amount of movement when opening and closing, and the corrugated structure of the slide valve bellows 10 enables it to adapt to this movement. The slide valve bellows 10 can also absorb vibrations and shocks caused by air flow or other movements, helping to prevent these forces from damaging the valve and other components. During the process of breaking the cavity of the ion source 12, the pressure difference with the rear end of the mass spectrometer may be large, and the structural design of the slide valve bellows 10 enables it to withstand these pressure differences.

[0246] The main function of the guide sleeve 11 is to ensure that the valve moves along the correct trajectory when opening and closing. This helps maintain the stability and accuracy of the valve, ensures that the sealing surfaces are correctly aligned, and prevents leakage. At the same time, the guide sleeve 11 is made of low-friction material to reduce friction when the valve moves. This helps to extend the life of the valve and ensure smooth movement.

[0247] The sealing rubber ring 17 is used to provide sealing performance when the valve is closed to prevent gas leakage. The sealing rubber ring 17 is responsible for filling the gap between the valve and the valve seat to ensure airtightness. The sealing rubber ring 17 used in the mass spectrometer is usually required to be temperature-resistant, corrosion-resistant, and radiation-resistant, and can maintain elasticity, have a long service life, and good sealing performance.

[0248] The ion flight flat tube adopts one-piece die-casting technology. The flight flat tubes of thermal ionization mass spectrometers on the market usually use welding technology. Welding usually requires connection points, and these connection points may be potential sources of leakage in the vacuum system. One-piece die-casting technology can create a joint-free, more uniform and continuous structure, thereby reducing potential leakage points and improving overall strength. In addition, one-piece die-casting technology can produce a more uniform surface and a smaller internal volume, which helps to improve sealing. One-piece die-casting technology uses one material for die-casting, which can completely avoid welding problems between different materials and significantly improve the material compatibility of the vacuum system and the long-term stability of the system.

[0249] Furthermore, in this embodiment, the detector cavity 15 and the detector cavity cover 16 are sealed with silver wire. Silver has good plastic deformation and ductility, and its thermal expansion coefficient is not much different from that of stainless steel. It is also cost-effective and easy to weld, and is a good sealing material. In large or non-standard flange seals, the use of silver wire for sealing has a much lower leakage rate after assembly than other sealing methods.

[0250] The Faraday cup moving device in the detector cavity 15 is controlled by a slide rail, and its controller is located in the cavity. Placing the controller inside can reduce the airtightness requirements of the external connection, thereby reducing the risk of gas leakage. In addition, in a vacuum environment, heat conduction and convection are almost eliminated, and temperature control is more stable, which helps to ensure the stable operation of the controller.

[0251] The vacuum sensor 5 is installed on the pump exhaust pipe, the ion source 12 cavity, and the ion flight pipeline. The vacuum sensor 5 connected to the pump exhaust pipe is used to monitor the pre-vacuum pressure in real time, and can determine whether the turbomolecular pump 2 can be turned on. The vacuum sensor 5 connected to the ion source 12 cavity is used to monitor whether the vacuum isolation valve can be opened after sample replacement, and monitor whether the lens high pressure can be opened. The vacuum sensor 5 connected to the ion flight pipeline is used to determine the cleanliness of the ion flight path during sample measurement.

[0252] The following is a detailed description of the operation process of this vacuum system:

[0253] 1. Vacuum system operation process:

[0254] Confirm that all connections of the instrument are correct and well sealed;

[0255] Turn on the oil-free rotary vane vacuum pump 1 to pump the ion source 12 chamber to a primary vacuum;

[0256] When the vacuum sensor 5 connected to the pump exhaust pipe shows that the vacuum is less than 10Pa, the turbomolecular pump 2 is turned on;

[0257] The vacuum sensor 5 connected to the ion source 12 cavity shows that the vacuum is less than 1×10 -4After Pa, turn on the vacuum sensor 5 connected to the ion flight pipeline.

[0258] The vacuum sensor 5 connected to the ion flight pipeline shows that the vacuum is less than 1×10 -4 After reaching Pa, turn on the ion pump and select the high pressure gear according to the actual situation.

[0259] 2. Partial venting of the ion source 12 cavity (maintenance, sample replacement process) Vacuum system operation process:

[0260] Close the vacuum isolation valve

[0261] Confirm that all connections of the instrument are correct and well sealed;

[0262] Turn off turbomolecular pump 2;

[0263] After the speed of turbomolecular pump 2 reaches 0, turn off the oil-free rotary vane vacuum pump 1 and vent it;

[0264] Open the ion source 12 cavity to complete the sample change.

[0265] Close the ion source 12 cavity and make sure that all parts of the instrument are connected correctly and well sealed;

[0266] Turn on the oil-free rotary vane vacuum pump 1 to pump the ion source 12 chamber to a primary vacuum;

[0267] When the vacuum sensor 5 connected to the pump exhaust pipe shows that the vacuum is less than 10Pa, the turbomolecular pump 2 is turned on;

[0268] After the vacuum sensor 5 connected to the cavity of the ion source 12 shows that the vacuum is less than 1×10-4 Pa, the vacuum isolation valve is opened.

[0269] 3. Baking procedure:

[0270] Before the vacuum system is baked, the whole instrument must be assembled and powered on, and a molecular pump must be used to complete the initial vacuum test. The vacuum should not be higher than 5×10 -4 Pa.

[0271] Before baking, remove the analysis electromagnet, wrap the vacuum chamber 8, the flight pipe and the connecting flange with aluminum foil, turn on the molecular pump and the oil-free rotary vane vacuum pump 1, and turn off the ion pump.

[0272] During the baking process, multiple sets of self-controlled high-quality insulating heating tapes are used to wrap the cavity and flight pipe. The detector cavity 15 and the ion source 12 cavity are powered on for heating and baking in sequence, and the corresponding baking temperatures are set according to the temperature requirements of different components. The ion pump baking mode is turned on. The detector baking temperature is 100°C, the flight pipe baking temperature is 130°C, and the ion source 12 cavity baking temperature is 110°C. The overall baking time is 24 hours until the vacuum degree no longer decreases.

[0273] After baking is completed, the temperature is gradually lowered from the ion source 12 cavity to the receiver cavity (at intervals of 30 minutes), the ion pump baking mode is turned off, and the heating tape and aluminum foil are removed.

[0274] Keep the molecular pump and ion pump pumping for no less than 12 hours, and record the vacuum degree of 8 in the vacuum chamber.

[0275] The following is a detailed description of the simulation process of the gas molecule motion behavior and pump selection in this vacuum system:

[0276] 1. According to the actual design of thermal ionization mass spectrometer, establish a high-precision three-dimensional model and a gas flow path model.

[0277] 2. In the gas molecule motion behavior simulation software, set relevant parameters, including: pump position, pump extraction speed, gas leakage rate at each flange port, material desorption parameters, etc.

[0278] 3. Select the mass spectrometer wall where the pressure needs to be observed or create a cross section in the model to calculate the flux, set the meshing method according to the finite element method, and set the pressure observation direction of the cross section.

[0279] 4. Run the simulation software to obtain and record the real-time wall pressure heat map, cross-sectional pressure curve, and the motion behavior of gas molecules inside the model.

[0280] 5. Set the pressure threshold for stopping the simulation, record the time from the start of the simulation to the end of the simulation, and evaluate the stability, effectiveness, and responsiveness of the vacuum system of the model.

[0281] 6. Among them, the software simulation calculation can obtain the relationship between wall pressure and pump extraction time heat map, interface average pressure and pump extraction time relationship curve, ideal ultimate vacuum value, the pumping time required to reach the ideal ultimate vacuum value, etc.

[0282] 7. Adjust the position of the pump, the pumping speed and other parameters in the model, observe the trend of the heat map and curve changes, compare the time from the start of the simulation to the end of the simulation, analyze the differences in the vacuum system under different models, and select the optimal model solution.

[0283] This vacuum system has the following advantages:

[0284] 1. Based on the simulation of gas flow behavior, this system studies the factors affecting the performance of each component in the vacuum system, such as the type, layout, and number of pumps, and uses more efficient and compact vacuum pump technology to optimize the realization of gradient vacuum and improve vacuum extraction speed and stability.

[0285] 2. During the manufacturing and installation of components, the vacuum system uses special casting and sealing technologies to improve the sealing performance of the vacuum system, effectively reduce potential leakage points, reduce the need for routine maintenance, and improve the stability of later use.

[0286] It is to be understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present invention, but the present invention is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A method for modeling gas flow behavior in a mass spectrometer vacuum system, characterized in that: The vacuum system of the mass spectrometer has a plurality of partitions, and the plurality of partitions are connected in sequence. The method comprises the following steps: obtaining partition information of a plurality of partitions in a vacuum system of a mass spectrometer; According to the partition information, a gas flow model of each partition is established respectively; According to the partition information and the gas flow model of each partition, an effective pumping speed model of each partition is established respectively; The effective pumping speed models of each partition are combined to obtain the gas flow behavior model in the mass spectrometer vacuum system.

2. The method according to claim 1, characterized in that The partition information includes gas characteristic parameters, geometric parameters and pumping speed characteristic parameters; The gas characteristic parameters include: gas viscosity η, gas density ρ, gas flow rate v, and gas pressure value p; The geometric parameters include: the equivalent diameter d of the partitioned pipeline cross section; The pumping speed characteristic parameters include: a pump inlet air pressure value, an air pressure value inside a partition, a volume flow value at the pump inlet, and a leakage rate within the partition.

3. The method according to claim 2, characterized in that The step of establishing the gas flow model of each partition according to the partition information includes: Analyze the airflow state in each partition according to the gas characteristic parameters and geometric parameters in the partition information; According to the airflow state in each partition, the gas flow model of each partition is established respectively.

4. The method according to claim 3, characterized in that The step of establishing a gas flow model for each partition according to the gas flow state in each partition includes: Determine in turn whether the airflow state in each partition is the first flow state or the second flow state: When the gas flow state in the partition is a first flow state, the gas flow state model adopts a Reynolds number expression, and the first flow state is a turbulent state; When the gas flow state in the partition is the second flow state, the gas flow state model adopts the Knudsen number expression, and the second flow state is a viscous flow, a molecular flow or a transitional flow state.

5. The method according to claim 4, characterized in that The Reynolds number expression is: Where Re is the Reynolds number; η is the gas viscosity; ρ is the gas density; v is the gas flow rate; The Knudsen number expression is: Where Kn is the Knudsen number; v is the gas flow rate; η is the gas viscosity; p is the gas pressure value; d is the equivalent diameter of the partitioned pipe cross section.

6. The method according to any one of claims 3 to 5, characterized in that: The effective pumping speed model includes: Q=P·S eff ·F(Kn) F(Kn)=1+α·Kn S eff =S0·(1-β·f(Re)) Q=P·S0·(1-β·f(Re))·(1+α·Kn) Where Q is the leakage rate in the partition; P is the pressure in the system; S eff is the effective pumping speed; F(Kn) is the correction term dependent on the Knudsen number; α is the slip correction coefficient; S0 is the nominal pumping speed of the pump; β is the transition flow correction coefficient; f(Re) is the correction function related to the Reynolds number.

7. The method according to claim 6, characterized in that The effective pumping speed model also includes: Δp=p 真空腔 -p 泵入口 =p c -p in In the formula, p in is the pump inlet pressure; p c is the internal air pressure value of the partition; S is the pumping speed; S eff is the effective pumping speed; is the volume flow rate value at the pump inlet.

8. A method for designing a mass spectrometer vacuum system, characterized in that: The steps include: Obtain the vacuum degree requirement value of each partition in the pump model database and the mass spectrometer vacuum system; According to the gas flow behavior modeling method according to any one of claims 1 to 7, a gas flow behavior model in a mass spectrometer vacuum system is obtained; The pumps for each partition in the mass spectrometer are selected according to the pump model database, the vacuum degree requirement value and the gas flow behavior model.

9. The method according to claim 8, characterized in that The step of selecting pumps for each partition in the mass spectrometer according to the pump model database, the vacuum degree requirement value and the gas flow behavior model specifically includes: According to the vacuum degree requirement value of the target partition, a pump that meets the first preset condition is selected from the pump model database; According to the gas flow behavior model, an effective pumping speed of the pump is obtained; According to the effective pumping speed of the pump, a pump that meets the second preset condition is selected from the pumps that meet the first preset condition, that is, the target pump model is obtained; Repeat the above steps until the pumps for all zones are selected.

10. The method according to claim 9, characterized in that The first preset condition is that the maximum vacuum degree of the pump is less than or equal to the utilization rate of the pump multiplied by the required vacuum degree, or the pump has a minimum residual pressure; The second preset condition is that the rated pumping speed of the pump is greater than or equal to the effective pumping speed.

11. A modeling device for gas flow behavior in a mass spectrometer vacuum system, characterized in that: include: A first acquisition unit, a first modeling unit, a second modeling unit and a first processing unit; The first acquisition unit is used to acquire partition information of multiple partitions in the vacuum system of the mass spectrometer; The first modeling unit is electrically connected to the first acquisition unit, and is used to establish a gas flow model of each partition according to the partition information; The second modeling unit is electrically connected to the first acquisition unit and the first modeling unit, respectively, and is used to establish an effective pumping speed model for each partition according to the partition information and the gas flow model of each partition; The first processing unit is electrically connected to the second modeling unit, and is used to combine the effective pumping speed models of each partition to obtain a gas flow behavior model in the vacuum system of the mass spectrometer.

12. The device according to claim 11, characterized in that The first processing unit includes an analysis module and an execution module. The analysis module is used to analyze the airflow state in each partition according to the gas characteristic parameters and geometric parameters in the partition information. The execution module is used to establish the gas flow state model of each partition according to the gas flow state in each partition.

13. A design system for a mass spectrometer vacuum system, characterized in that: include: A second acquisition unit, a second processing unit and a modeling device for gas flow behavior in a mass spectrometer vacuum system according to claim 11 or 12; The second acquisition unit is used to acquire the vacuum degree requirement value of each partition in the pump model database and the mass spectrometer vacuum system; The gas flow behavior modeling device in the mass spectrometer vacuum system is used to establish a gas flow behavior model in the mass spectrometer vacuum system; The second processing unit is electrically connected to the second acquisition unit and the gas flow behavior modeling device in the mass spectrometer vacuum system, and is used to select pumps for each partition in the mass spectrometer based on the pump model database, the vacuum requirement value and the gas flow behavior model.

14. A mass spectrometer vacuum system, characterized in that: include: Ion source area, analysis area, detector area, oil-free rotary vane vacuum pump, turbomolecular pump and ion sputtering pump; The ion source area, the analysis area and the detector area are connected in sequence, the oil-free rotary vane vacuum pump and the turbomolecular pump are both connected to the ion source area, and the ion sputtering pump is connected to the analysis area; The oil-free vane vacuum pump, the turbomolecular pump and the ion sputtering pump are selected by using the design method for a mass spectrometer vacuum system according to any one of claims 8 to 10.

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